Nanoporous ultrafine alpha-alumina powders and sol-gel process of preparing same

ABSTRACT

The present invention provides α-alumina powders comprising α-alumina particles of which at least 80% of the α-alumina particles have a particle size of less than 100 nm. The invention also provides slurries, particularly aqueous slurries, which comprise α-alumina powders of the invention. The invention further provides methods of manufacturing α-alumina powders and α-alumina slurries of the invention and methods of polishing using same.

FIELD OF THE INVENTION

The present invention relates to nanosized α-alumina particles andmethods of making same and more particularly to nanosized α-aluminaparticles having an average particle size of less than about 100 nm. Thepresent invention also relates to chemical mechanical polishingcompositions (CMP) comprising α-alumina particles of the invention andCMP polishing methods using same.

BACKGROUND OF THE INVENTION

Ultra-fine alumina (aluminum oxide) powder is one of the most widelyused ceramic materials in a variety of industries. Applications of finealumina powders include use as abrasives for polishing semiconductor andprecision optical components, catalyst supports including the supportstructure in automobile catalytic converters, fillers for polymers, andpigment for painting, and the like. Alumina has over twelve (12)different crystalline phases, each of which has a different latticestructure and physical properties. However, the most well known andcommonly used alumina powders are γ-alumina and α-alumina. The lowtemperature phase, γ-alumina, is thermodynamically metastable andtransforms to the thermodynamically stable phase, α-alumina, attemperatures in excess of about 1100° C. or about 1200° C. depending onvarious conditions. With a defective spinel structure, γ-alumina powdercan have very small particle sizes, e.g., particle sizes of less thanabout 20 nm, and extremely high surface area, e.g., greater than about300 m²/g. Moreover, γ-alumina can be processed via both vapor and liquidphase processing techniques. Ultrafine γ-alumina having an averageparticle size of less than 40 nm and a polishing slurry with γ-aluminaare commercially available.

The density of α-alumina is about 20% higher than the density ofγ-alumina and more chemically and mechanically durable than γ-alumina.Thus, nanosized α-alumina particles should be suitable for a greaterrange of applications than nanosized γ-alumina. However, during thephase transformation, due to the reorganization of oxygen in the crystallattice, the alumina particle size increases drastically such thatα-alumina prepared from γ-alumina normally has a particle size ofgreater than 100 nm.

To make nanosized α-alumina, e.g., α-alumina particles of less thanabout 100 nm, has been a challenge for an extended period of time. Toprevent the particle from rapid grain growth is the key. It is wellknown that fine α-alumina powders having an average particle size ofgreater than 100 nm can be prepared via a seeded sol-gel process. In theprocess, boehmite is first peptized in acidic aqueous solution,containing nitric acid or acetic acid and then a couple of weightpercent of α-alumina seeds, usually fine α-alumina particles, are addedto the solution during the peptization to allow phase transformation tooccur at lower temperature. The sol is oven dried at about 100° C. andconverted to a dry gel. After crushing to micron sized granules, theyare fired at a high temperature, normally over about 1000° C. to theproduce of α-alumina particles. The temperature must be well controlledto prevent particle growth. However, in this process micron sized grainsremain intact during the phase transformation process and result inmechanically strong hard grains of α-alumina after completion of thetransformation. To make nanoalumina particles, high mechanical energy isrequired to crush or break down the grain into primary particles whichtypically have an average particle size of more than 100 nm. Moreover,the grinding process frequently results in high levels of impuritycontamination.

U.S. Pat. No. 5,312,791 recites a modified approach to prepare aluminagrains and fibers. The starting material is boehmite that is peptizedand then dispersed in water to generate an alumina sol. The sol israpidly cooled in liquid nitrogen or, alternatively slowly cooled byfreeze drying. Water is sublimed under vacuum from the sol to form a gelcomposed of flakes having a thickness of between 1 and 3 μm. By theprocess recited in '791 patent, finer aluminal powders, flakes, fibers,and grains can be made having micron-sized smallest dimensions. However,as the powders themselves have no porosity, they require high mechanicalenergy grinding to form smaller particles which introduces high levelsof impurities into the α-alumina product.

Methods of making α-alumina particles or grains using Seeded Gel (SG)technology via controlled solution chemistry has been known for severaldecades. Typically the process includes peptization of boehmite powder(AlOOH) in water by the addition of an acid, such as nitric acid,hydrochloric acid, or acetic acid, to form a uniform boehmite sol.Alumina seeds which are frequently fine α-alumina particles, which havebeen dispersed in water, are added to the boehmite sol and the admixtureis combined thoroughly. The sol solution is then subjected to a dryingprocess to transform the sol into a dried gel which is then pulverizedand fired to a temperature at which point transformation to α-alumina iscompleted with minimal sintering. Because of the presence of the seedparticles, transformation temperature is decreased from about 1200 toabout 1250° C. for unseeded sols to about 1000 to about 1050° C. Theα-alumina thus prepared can have sub micron particle sizes. However, noα-alumina particles prepared to date have an average particle size ofless than about 100 nm.

SUMMARY OF THE INVENTION

This invention provides a technique to make stable nanosized α-aluminaparticles. The invention further provides nanosized α-alumina powdersand slurries comprising same which comprise no or very little chemicaladditives for suspension stability. The slurry of the invention providesa high material removal rates on silicon dioxide (SiO₂) and furtherprovides very good surface finishing. The method of manufacture of thenanosized α-alumina powders of the invention comprise seeding withnanosized α-alumina seed particles and firing the seeded alumina gel atreduced temperatures.

The present invention provides an α-alumina powder comprising α-aluminaparticles of which at least 80% of the particles have a particle size ofless than 100 nm. The invention further provides slurries comprising atleast one α-alumina powder of the invention. That is, the inventionprovides a slurry comprising α-alumina particles of which at least 80%of the α-alumina particles have a particle size of less than 100 nm.

The invention also provides a process for the producing the α-aluminaparticles and powders of the invention. The process comprises the stepsof:

providing a gel comprising at least one alumina precursor and aplurality of α-alumina seed particles;

drying the gel;

firing the dried gel at a temperature capable of inducing α-aluminaformation without causing particle size growth.

In yet another embodiment, the invention provides polishing methodswhich include the use of α-alumina powders and slurries as a polishingagent. The polishing method comprises the steps of:

providing slurry comprising α-alumina particles of which at least 80% ofthe α-alumina particles have a particle size of less than 100 μm; and

applying the slurry to an interface between the substrate and apolishing pad.

Other aspects and embodiments of the invention are discussed below.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a micrograph of α-alumina particles of the invention preparedfrom aluminum nitrate and 10% α-alumina seeds by weight and fired at900° C. for 1 hour (200 nm scale bar); and

FIG. 2 is a micrograph of α-alumina particles of the invention preparedfrom aluminum sec-butoxide and 10% α-alumina seeds by weight and firedat 850 C for 1 hour (100 nm scale bar).

DETAILED DESCRIPTION OF THE INVENTION

The α-alumina particles and slurries comprising same provided by thepresent invention are suitable for use in various applicationsincluding, for example, polishing, CMP applications, catalyst supportmaterials, and the like. The α-alumina particles and slurries areparticularly suited for use in polishing and CMP applications becauseα-alumina particles of the invention possess exceptional hardness andhave an average particle size of between 10 nm and about 100 nm.Moreover, the α-alumina particles of the invention offer high materialremoval rates with minimal substrate defectivity.

The present invention provides α-alumina powders in which at least 80%of the α-alumina particles of the powder have a particle size of lessthan 100 nm. The present invention further provides slurries comprisingat least one α-alumina powder of the invention. Preferably, about 90% ofthe α-alumina particles in the powders or slurries of the invention havea size of between about 10 nm and about 100 nm. More preferably about99% of the α-alumina particles in the powders or slurries of theinvention have a size of between about 10 nm and about 100 nm. Inparticularly preferred embodiments of the invention, about 99% of theα-alumina particles in the powders or slurries of the invention have asize of between about 25 nm and about 80 nm, or between about 30 nm andabout 70 nm.

In other preferred embodiments, the invention provides α-alumina powderswhich comprise α-alumina particles having at least 99% of the particleswithin a size distribution of about 10 nm.

Other preferred slurries of the invention comprise one or more α-aluminaparticles of the present invention. That is, slurries of the inventioncan comprise a single particle size of α-alumina or a composite mixtureof two or more particles sizes having different average particle sizeswhich when mixed combine to form a mono-modal, bi-modal, or poly-modalparticle size distribution. Typically slurries comprising α-aluminaparticles having a single average particle size distribution arepreferred.

Preferred slurries of the invention comprise one or more α-aluminaparticles of the invention. Preferred α-alumina particles include anyα-alumina particle described herein. More preferred slurries includethose slurries in which the α-alumina particles are dispersed in anaqueous mixture. Preferred aqueous mixtures include water, particularlydeionized or distilled water, aqueous solutions comprising one or moresurfactants, organic acids, or other additives. Preferred additives arechemically inert to α-alumina under storage or polishing conditions.Additionally preferred additives are capable of inhibiting aggregationof α-alumina particles in an aqueous mixture. Particularly preferredadditives to the aqueous mixture include organic acids such as aceticacid, formic acid, lactic acid, glycolic acid, citric acid, oxalic acid,and other carboxylic acids having less than about 6 carbon atoms.

Aqueous slurries of the present invention typically have a pH of betweenabout 2 and about 11. In certain preferred applications, slurries havingan acidic pH or an alkaline pH are desirable. Thus more preferredaqueous slurries of the invention have a pH of from about 1 or 2 toabout 6 or between about 8 and about 10.5.

The slurries of the invention are suitable for use in a variety ofapplications including use as abrasives in polishing or CMPapplications, as supports for metal catalysts and the like.

In the process of the invention, aluminum chemicals are used as theα-alumina precursor, e.g. molecular alumina precursors are utilizedinstead of boehmite. The aluminum compounds can be inorganic (Aluminumnitrate, aluminum chloride, aluminum sulfate, and the like) or organic(aluminum alkoxides, aluminum acetate, and the like). Preferably, theinorganic or organic aluminum compounds which are utilized as molecularalumina precursors are water soluble.

In preferred embodiments, a process for the production of α-aluminaparticles is provided which comprises the steps of

providing a gel comprising at least one alumina precursor and aplurality of α-alumina seed particles;

drying the gel;

firing the dried gel at a temperature capable of inducing α-aluminaformation without causing particle size growth.

It is generally desirable to have the seed particles substantiallyhomogeneously dispersed throughout the gel to insure efficient seedingof the gel during firing.

In particularly preferred processes of the invention, the gel, whichcomprises at least one alumina precursor and a plurality of α-aluminaseed particles, is prepared by the process comprising the steps of:

providing an aqueous solution of at least one molecular aluminaprecursor which has α-alumina seed particles dispersed therein

concentrating the aqueous solution to forma a gel having the α-aluminaseed particles dispersed therein.

In preferred embodiments, the firing step is carried out a temperaturewhich is sufficient to transform the gel to the α-alumina phase but isinsufficient to induce sintering of the gel or an increase in individualparticle size. Typically preferred processes of the invention comprise afiring step conducted at a temperature of less than about 1050° C. ormore preferably at a temperature of less than about 950° C. Inparticularly preferred processes of the invention the firing isconducted at a temperature of between about 750° C. and about 950° C. orbetween about 800° C. and about 900° C.

Although any water soluble organic or inorganic coordination complex orsalt of aluminum may be suitable for use in the processes of theinvention, preferred molecular alumina precursors are selected fromaluminum salts comprising one or more anions selected from alkoxides,aryl oxides, carboxylates, halides, sulphate, nitrate, oxalates, andacetoacetonates. Particularly preferred molecular alumina precursorsinclude aluminum alkoxides, carboxylates, halides and nitrates.

Preferred aqueous solutions provided or prepared by the processes of theinvention comprise water, at least one molecular alumina precursor, atleast one acid, and α-alumina seed particles. Preferred acids areselected from the group consisting of nitric acid, sulfuric acid,hydrochloric acid, hydrobromic acid, hydroiodic acid, acetic acid,formic acid, propionic acid and the like.

At present no uniform α-alumina particles having an average particlesize of less than 125 nm or less than 100 nm are available for use asseeds in the methods of making nanosized α-alumina particles of theinvention. Thus, an iterative process is typically undertaken wherebyinitial nanosized α-alumina particles are prepared by using slightlylarger seed α-alumina particles to form a product α-alumina comprisingnanosized α-alumina having a particle size of less than 100 nm and seedparticles having a particle size of about 125 nm or more (typicallyabout 1 to about 5 or 10 weight percent of the product α-aluminaparticles are seed particles). Repeatedly using product nanosizedα-alumina particles as the seed α-alumina particles in future productionruns reduces the concentration of larger α-alumina particles. Forexample, at a five (5) weight percent loading of seed particles, afterfour production runs the concentration of original α-alumina particleseeds, e.g., particles of greater than about 125 nm, is about 6 ppm. Theconcentration of larger α-alumina particles will continue to decreaseuntil α-alumina particles with substantially uniform particle sizes areobtained.

In preferred aqueous solutions, the α-alumina seed particles have anaverage particle size of less than about 125 nm, or more preferably lessthan about 100 nm. Particularly preferred seed particles have an averageparticle size of between about 30 nm and about 100 nm, between about 40nm and about 80 nm, or between about 50 nm and about 70 nm.

Seed α-alumina particles are well dispersed in water and then thealuminum compounds are added to the water dispersion of the seedparticles. It is desirable to increase the seeding efficacy of the waterdispersion. Thus the concentration of the seeds is relatively high toincrease the seeding power of the solution, e.g., the ratio of aluminumatoms in the product α-alumina particles originating in the seed versusthe molecular alumina precursor is typically between about 1:3 and about1:1000 or more preferably between about 1:6 and about 1:20. In preferredembodiments, the seed particles comprise between about 0.1 and about 15weight percent of the product α-alumina powder. In particularlypreferred embodiments the concentration of the seeds is about 1 and 10%by weight of the product α-alumina.

Applicants have discovered that the use of smaller seed particlestypically result in a gel having a lower transformation temperature andproduct α-alumina powders comprising smaller particles. Moreover,smaller seed particles typically possess greater seeding power, e.g.,fewer seeds are needed to induce crystal formation or phasetransformation to α-alumina. I

The pH of the dispersion of seed α-alumina particles before addition ofthe molecular alumina precursor is typically between 6 and 7. Aftersolvation of the molecular alumina precursor, the pH of the dispersionfrequently drops to less than about 2 or even to less than about 1. Thedispersion can be optionally heated or aged at elevated temperature,e.g., greater than 90° C., to evaporate water. Typically theconcentration step, e.g., heating and/or aging of the dispersion, isconducted with mechanical mixing to prevent deposition of the seedparticles. After the viscosity of the dispersion is sufficient toprevent seed particle deposition, the dispersion is cooled to roomtemperature to form the gel. The gel can then be fired in air at atemperature of less than about 1050° C. or more preferably between about800° C. and about 900° C. to transform the alumina gel to α-alumina.

Typically alkaline chemicals such as ammonia can be added to the abovesolution before aging and/or concentration of the solution. Although notwishing to be bound by theory, the addition of an alkaline additive suchas ammonia or urea is necessary to initiate gel formation. However, therate and quantity of alkaline added to the solution must be carefullyregulated because addition of excess alkaline can induce formation ofBayerite. Preferably the alkaline chemical(s) are gradually added to thedispersion to facilitate hydrolysis at an elevated temperature, e.g.,about 70° C. Hydrolysis with ammonia typically results in the formationof boehmite.

In general, when ammonia and other basic additives are preferably usedin conjunction with aluminum salt precursors. However when alkalinechemicals such as ammonia are added to the dispersion it is necessary tocontrol the pH of the dispersion because bayerite (Al(OH)₃) formation ispossible at a pH greater than about 5. After addition of ammonia andresultant increase in pH, the dispersion becomes increasingly viscousand finally forms a gel. Preferably the pH of the reaction is maintainedat a pH of between about 4 and about 4.5 during the gelation process.The gel is then subjected to firing to transform the gel to α-alumina asdiscussed supra.

Applicants have surprisingly discovered that substitution of urea forammonia as the alkaline chemical facilitating hydrolysis permits reducedfiring temperatures. Typically, when urea is used as the alkalinechemical additive, hydrolysis is carried out at a temperature of morethan 90° C. The alumina gel formed by the process using urea may befired to transform to α-alumina at reduced firing temperatures, e.g., ata temperature of about 800° C.

In another embodiment, gel formation using one or more aluminumalkoxides as the molecular alumina precursor required an aqueoushydrolysis at an elevated temperature and further frequently requiresthe addition of an acid catalyst such as hydrochloric acid or nitricacid. The aluminum alkoxide precursor can be solvated in an anhydrousalcohol and then mixed with an aqueous dispersion of the seed particlesor alternatively the aluminum alkoxide may be directly solvated in theaqueous dispersion of seed crystals. Acid added to the aqueousdispersion catalyzes the hydrolysis of the aluminum alkoxide and furtherfacilitates peptization of the dispersion. The sol is kept stirring atan elevated temperature until it is sufficiently viscous to preventsedimentation of the seed particles.

Hydrolysis of the aluminum alkoxide can be conduced at either roomtemperature or at an elevate temperature. When the hydrolysis is carriedout at room temperature, the resultant sol is amorphous, e.g., a pseudoboehmite solution with an alcohol layer on top of an aqueous phase.Preferably the hydrolysis is carried out at a temperature sufficient tocomplete the hydrolysis within about 24 hours. Typically preferredhydrolysis reactions are carried out at a temperature of between about50° C. and about 90° C. Alcohol is removed by evaporation from thereaction mixture. Typically, it is preferably to have a rapid rate ofhydrolysis in order to minimize seed particle aggregation.

Alternatively, when hydrolysis is carried out at an elevatedtemperature, e.g., about 50° C. to about 80° C. The product produced bycarrying out hydrolysis at room temperature is substantially the same asthe product formed at elevated temperature but the rate of hydrolysis istypically too slow to be practical.

Firing of gels prepared from sols of hydrolyzed aluminum alkoxideprecurors provides α-alumina particles at a temperature of between about800 to about 850° C.

The present invention provides new processes of preparing α-aluminaparticles which comprise firing of a precursor gel at a temperature ofbetween about 750° C. and about 950° C. or more preferably between about800° C. and about 900° C. depending upon the molecular aluminaprecursor. The low transformation temperatures for formation ofa-alumina are desirable and advantageous, in part because they preventparticle growth during firing and excessive necking of particles, e.g.,particle sintering. Applicants have surprisingly discovered thatsubstantially uniform dispersion of nanosized α-alumina seed particlesthroughout the sol, the seeding power is maximized thereby reducing thetransformation temperature.

A comparison study on a boehmite, P2K of Condea, with the same aluminaseeds, same concentration (10%) showed that P2K requires much highertemperature for the phase transformation. When fired at 900° C. for 1hour only about 40% of α-Al₂O₃ is formed form the P2K material incomparison to about 100% of α-Al₂O₃ from the process of the invention.

SEM shows that the crystallite (or primary particle) size for the powdermade from the chemical is definitely around about 50 nm (See FIGS. 1 and2). Though the aprticles are slightly agglomerated and necked, the SSAis 39 m²/g for a sample fired at 900° C. for 1 hour. In comparison,α-alumina prepared from P2K under the same firing conditions results inabout α-alumina particles having an average particle size of about 100nm and a SSA of less than 24 m²/g.

The α-alumina particles, α-alumina powders, and α-alumina slurries ofthe present invention provide a very pure form of α-Al₂O₃. No dopants,sodium, silicon dioxide or the like are utilized during the productionprocess. Moreover, the milling of the fired gel to generate theα-alumina particles having an average particle size of less than 100 nmis facile resulting in minimal contamination from the milling process.

EXAMPLE 1

Polycrystalline α-alumina particles were dispersed in water by highenergy attrition milling using high purity alumina media as the millingmedia. The slurry such prepared was used as seeds (27.5%) for thefollowing processing for nanosized alumina. 42.5 g of the seeds slurrywas mixed with 2130 g of DI water and 62.3 g of nitric acid (˜70%) undervigorous stirring using a mixer. To the solution, 577 g of commercialaluminum sec-butoxide was added and stirred for 2 hours at roomtemperature. The solution was further heated up to temperature 80 Cunder vigorous stirring and maintained at the temperature until gelationtaked place. The gel was transferred to a stainless container and driedin an oven at 80C. The dried gel was fired in a box furnace at 880 C for1 hour and cooled down to room temperature. The fired material wasconfirmed to be ˜98% α-alumina powder on X-ray diffraction and Hedensity measurement. SEM showed that the primary particle is 40-60 nm insize. The fired powder was charged into the same attrition miller withwater and milled for 6 hours using the alumina milling media. The sizedistribution of the milled slurry measured by a dynamic Horiba particlesize analyzer and gave a D50=76 nm.

EXAMPLE 2

127.5 g of the same α-alumina seeds as in Example 1 was mixed with 6350g of water and 561.5 g of HCl (35%) in a Teflon lined stainlesscontainer. On the other hand, 1730 g of aluminum butoxide was mixed with5100 g of anhydrous ethanol in a glass container. The two solutions werefurther mixed in the Teflon lined stainless container and stirredvigorously on a hotplate. The solution was heated up to 80 C slowly andmaintained at the temperature until the solution becomes viscous. Thegel-like material is transferred to a stainless pan and dried in adrying oven. The dried material was fired at 820 C for 1 hour in a boxfurnace. The fired powder was confirmed to be ˜98% of α-alumina based onX-ray and He-density measurements, with surface area of the powder being45 m2/g. SEM shows that the primary particles are 40-60 nm in size. Thepowder was dispersed in DI water and charged in an attrition miller andmilled for 6 hours. The milled particles had a D50˜75 nm, based on adynamic particle size analyzer.

EXAMPLE 3

120 g of the alfa-alumina seeds, as same as in Example 1, was dispersedin 5000 g of DI water, to which 3000 g of hydrous aluminum nitrate wasadded. The solution was heated on a hotplate to temperature 75 C. 1540 gof ammonium hydroxide (28-30%) was drop wise added to the solution undervigorous stirring. The solution was stirred at the temperature until itbecame too viscous to stir. After dried in an oven, the gel-likematerial was first fired at 500 C to remove the NOx and then fired at880 C to complete the transformation to alfa-alumina. The fired powderwas confirmed to be ˜95% alfa-alumina based on X-ray diffraction andHe-density measurement. The specific surface area was 38 m2/g from a BETmeasurment. On SEM, the primary particles are 50-70 nm in size. Thefired powder was mixed with DI water and milled in an attrition millerusing a high purity alumina media. The milled slurry gave a D50˜75 nm,from on a dynamic particle size analyzer.

EXAMPLE 4

120 g of alfa-alumina seeds, 27.5% by solids same as in Example 1, wasmixed with 5000 g of DI water, to which 3000 g of hydrous aluminumnitrate, Al(NO₃)3.9H₂O was added. The solution was vigorously stirredusing a mixer and gradually heated on hot plate to a temperature of 85C. The solution was kept stirring at the temperature to evaporize thewater until solidification occurred. The material was cooled down toroom temperature, and then fired at 500 C to remove NOx. The pre-firedpowder was then fired at 880 C in a box furnace to complete thetransformation to alfa-alumina, which was confirmed as in Examples 1-3.The fired alumina powder was milled using an attrition miller for 6hours.

Although a number of embodiments of the present invention have beendescribed, it will become obvious to those of ordinary skill in the artthat other embodiments to and/or modifications, combinations, andsubstitutions of the present invention are possible, all of which arewithin the scope and spirit of the disclosed invention.

1-40. (canceled)
 41. An α-alumina powder comprising α-alumina particlesof which at least 99% of the particles have a particle size of betweenabout 25 nm and about 80 nm.
 42. The α-alumina powder of claim 41,wherein about 99% of the α-alumina particles have a size of betweenabout 30 nm and about 70 nm.
 43. The α-alumina powder of claim 41,wherein at least 99% of the α-alumina particles have a size within abouta distribution of about 10 nm.
 44. The α-alumina powder of claim 41,produced without silicon dioxide.
 45. The α-alumina powder of claim 41,produced without dopants, sodium, or silicon dioxide.
 46. The α-aluminapowder of claim 41, produced from an α-alumina precursor, the α-aluminaprecursor being an aluminum chemical.
 47. The α-alumina powder of claim46, wherein the aluminum chemical is selected from aluminum nitrate,aluminum chloride, aluminum sulfate, aluminum alkoxides, and aluminumacetate.
 48. The α-alumina powder of claim 46, wherein the aluminumchemical is a molecular alumina precursor.
 49. The α-alumina powder ofclaim 48, wherein molecular alumina precursor is selected from aluminumsalts comprising one or more anions selected from alkoxides, aryloxides, carboxylates, halides, sulphate, nitrate, oxylates, andacetoacetonates.
 50. The α-alumina powder of claim 48, wherein molecularalumina precursor is selected from aluminum alkoxides, carboxylates,halides, and nitrates.
 51. A slurry comprising α-alumina particles ofwhich at least 99% of the α-alumina particles have a particle size ofbetween about 25 nm and about 80 nm.
 52. The slurry of claim 51, whereinabout 99% of the α-alumina particles have a size of between about 30 nmand about 70 nm.
 53. The slurry of claim 51, further comprising water.54. The slurry of claim 51, further comprising deionized water.
 55. Theslurry of claim 51, further comprising one or more additives.
 56. Theslurry of claim 55, wherein the additives are chemically inert toα-alumina under storage conditions or polishing conditions.
 57. Theslurry of claim 55, wherein the additives inhibit aggregation ofα-alumina particles under storage conditions or polishing conditions.58. The slurry of claim 55, wherein the additive is selected fromorganic acids.
 59. The slurry of claim 58, wherein the additive isselected from acetic acid, formic acid, lactic acid, and citric acid.60. The slurry of claim 51, wherein the pH of the slurry is betweenabout 2 and about
 11. 61. The slurry of claim 51, wherein the pH of theslurry is between about 1 and about
 6. 62. The slurry of claim 61,wherein the pH of the slurry is between about 8 and about 10.5.
 63. Aprocess for the production of α-alumina particles which comprises thesteps of providing a gel comprising at least one alumina precursor and aplurality of α-alumina seed particles; drying the gel; and firing thedried gel at a temperature capable of inducing α-alumina formationwithout causing particle size growth; whereby α-alumina particles ofwhich at least 99% of the particles have a particle size of betweenabout 25 nm and about 80 nm are produced.
 64. The process of claim 63,wherein the gel comprising at least one alumina precursor and aplurality of α-alumina seed particles is prepared by the processcomprising the steps of: providing an aqueous solution of at least onemolecular alumina precursor which has α-alumina seed particles dispersedtherein; and concentrating the aqueous solution to forma a gel havingthe α-alumina seed particles dispersed therein.
 65. The process of claim64, wherein the α-alumina seed particles are homogeneously dispersed inthe gel.
 66. The process of claim 63, wherein the firing is conducted ata temperature of less than about 1050° C.
 67. The process of claim 63,wherein the firing is conducted at a temperature of less than about 950°C.
 68. The process of claim 63, wherein the firing is conducted at atemperature of between about 750° C. and about 950° C.
 69. The processof claim 63, wherein the firing is conducted at a temperature of betweenabout 800° C. and about 900° C.
 70. The process of claim 63, wherein themolecular alumina precursor is selected from aluminum salts comprisingone or more anions selected from alkoxides, aryl oxides, carboxylates,halides, sulphate, nitrate, oxalates, and acetoacetonates.
 71. Theprocess of claim 63, wherein the molecular alumina precursor comprisesone or more anions selected from alkoxides, carboxylates, halides andnitrate.
 72. The process of claim 63, wherein the α-alumina seedparticles have an average particle size of less than about 125 nm. 73.The process of claim 63, wherein the α-alumina seed particles have anaverage particle size of less than about 100 nm.
 74. The process ofclaim 63, wherein the α-alumina seed particles have an average particlesize of between about 30 nm and about 100 nm.
 75. The process of claim63, wherein the α-alumina seed particles have an average particle sizeof between about 40 nm and about 80 nm.
 76. The process of claim 63,wherein the α-alumina seed particles have an average particle size ofbetween about 50 nm and about 70 nm.
 77. The process of claim 63,wherein the ratio of α-alumina seed particles to molecular aluminaprecursor is between about 1:2 and about 1:1000 based on the ratio ofaluminum atoms in the seed particles and precursor.
 78. The process ofclaim 77, wherein the ratio of α-alumina seed particles to molecularalumina precursor is between about 1:6 and about 1:20.
 79. The processof claim 64, wherein the aqueous solution comprises water, at least onemolecular alumina precursor, at least one acid, and α-alumina seedparticles.
 80. The process of claim 79, wherein the acid is selectedfrom the group consisting of nitric acid, sulfuric acid, hydrochloricacid, hydrobromic acid, hydroiodic acid, acetic acid, formic acid,propionic acid, and citric acid.
 81. The process of claim 63, whereinthe α-alumina particles are produced without silicon dioxide.
 82. Theprocess of claim 63, wherein the α-alumina particles are producedwithout dopants, sodium, or silicon dioxide.
 83. A method of polishing asubstrate, the method comprising the steps of: providing slurrycomprising α-alumina particles of which at least 99% of the particleshave a particle size of between about 25 nm and about 80 nm; andapplying the slurry to an interface between the substrate and apolishing pad.